In the United States alone, hundreds of millions of pounds of mushrooms are produced and eaten annually. The most commonly grown species in the United States is Agaricus bisporus(the button mushroom). Other common mushroom species include Lentinus edodesShiitake), and Pleurotus ostreatus(oyster mushroom).
Mushrooms represent an important flavor component in food. One application of mushrooms in food preparations is as a dehydrated flavor product. Dehydrated mushroom products are used in dehydrated consumer foods such as soups and sauces, as a natural consumer flavoring product for cooking at home, and as an industrial flavoring material for a myriad of prepared foods. Development of improved, more highly flavored, dehydrated mushroom and mushroom products could greatly enhance the total market for mushroom production. In addition, by creating new and enhanced-flavored, dehydrated mushroom products, such as mushrooms with a meaty, savory and umami flavor, entirely new applications for dehydrated mushrooms could be created.
In order to effectively increase the flavor of a dehydrated mushroom, two metabolic events must occur. First, the amount of total unsaturated fatty acids in the mushroom tissue must be increased. The flavor of mushrooms is attributed, in part, to a variety of fatty acid oxidation products. D. A. Cronin, J. Sci. Fd Agric.(1971) 22:477. Increasing the fatty acid content in mushrooms is, therefore, needed to enhance the flavor content of mushrooms. Secondly, the activity of enzymes that oxidize fatty acids to oct-1-ene-3-ol and other volatile oxidation products associated with mushroom flavor and other meaty, savory flavors must be increased.
In order to induce these two metabolic events, delayed-release nutrients must be used in combination with a comprehensive cultural plan designed to assure an increase in lipid substrates and the stimulation of enzymatic activity.
Mushrooms are generally grown on a compost consisting of a complex of organic materials developed by the chemical and microbial degradation of such raw materials as straw, horse manure, chicken manure, cottonseed meal, and gypsum. The compost is pasteurized in an indoor environment and controlled for CO.sub.2, air flow, temperature and pH conditions. In order to produce mushrooms, the compost is inoculated with a vegetative mycelia of the fungus. The vegetative mycelial are allowed to grow for a period of approximately two weeks at temperatures between about 71.degree. F. and 79.degree. F.
During the final growth period when the familiar mushroom fruit body is produced, the compost is covered with "casing", a 11/2 inch layer of moist peat moss that contains limestone as a buffering agent. The temperature and CO.sub.2 levels are lowered during this period in order to induce mushroom fruit body growth. This process is known as "flushing."
During the final growth period, the mycelia that have grown into the casing layer start to form clusters of thickened hyphal strands called rhizomorphs. The rhizomorph is the support tissue upon which the fruiting body, or sporophore grows. The first fruiting bodies are harvested approximately three weeks after the casing is introduced.
Mushroom yields have been enhanced by the addition of vegetable oils at the time of spawning. U.S. Pat. No. 4,421,543. However, the grower must admix raw nutrients into the compost which is already colonized by vegetative roycelia. Introduction of the raw nutrients into the compost causes a rapid increase in metabolic heat which can make it difficult to keep the compost below 90.degree. F. in order to avoid killing the roycelia. Control of the metabolic heat requires an extra processing step that is disruptive to the grower.
At present, a nutrient supplement is needed that can be introduced without disrupting mushroom growth that increases the lipid content of mushrooms, thereby increasing the mushrooms' flavor capacity.
Four general reactions control the color and flavor created in a dehydrated mushroom during the dehydration process. These reactions are: (1) lipoxygenase enzyme oxidations, (2) polyphenol oxidase enzyme reactions, (3) Maillard browning reactions, and (4) Strecker degradation.
Lipoxygenase reactions convert fatty acids into a series of volatile compounds such as oct-1-en-3-ol and oct-1-ene-3-one. These compounds are responsible for the mushroom, musty, earthy, and savory flavors. Polyphenol oxidase is responsible for the oxidative browning of the mushroom by the formation of melanins from tyrosine and phenylalanine and forms tannins and other compounds contributing to astringency and bitter flavors. Maillard browning is a non-oxidative series of browning reactions between reducing sugars and amino acids that produces dark polymers and flavor compounds such as furfurals which impart nutty and meaty flavors. Strecker degradation of amino acids forms pyrazines, and organic sulfides which add other meaty, nutty, and chocolate notes.
In order to control the resulting flavor of the dehydrated mushrooms, one must control the degree to which the mushrooms undergo lipoxygenase enzyme oxidations, polyphenol oxidase enzyme reactions, Maillard browning reactions, and Strecker degradation. At present, a method is needed for producing differently flavored mushrooms by controlling the extent to which the mushrooms undergo these four reactions.